Nitrate-nitrogen isotopic patterns in surface waters of the western and central equatorial pacific     

Chisato Yoshikawa  Yasuhiro Yamanaka  Takeshi Nakatsuka 《Journal of Oceanography》2006,62(4):511-525

To understand the processes transporting nitrate to the surface layer of the western and central equatorial Pacific, we measured the nitrogen isotopic ratio of nitrate (δ ¹⁵NO ₃ ⁻ ), which is a very useful tracer of the source of nitrate, above 200 m depth in this region in December 1999. δ ¹⁵NO ₃ ⁻ is higher (about 13.0‰) in the surface water than in the subsurface water (where it is about 6.5‰) due to isotopic fractionation during nitrate uptake by phytoplankton. The δ ¹⁵NO ₃ ⁻ value has a roughly linear relationship with the natural logarithm of nitrate concentration (ln[NO ₃ ⁻ ]). However, for values above 150 m depth, the intercept of this linear relationship varies with position from east to west. On the other hand, the data at 200 m depth at all observation stations are concentrated around a single point (ln[NO ₃ ⁻ ] = 2.5 and δ ¹⁵NO ₃ ⁻ = 6.5‰) and do not fit the linear relationships for the shallower values. To examine the meaning of the observed distributions of δ ¹⁵NO ₃ ⁻ and nitrate concentration we developed a box model including nitrogen and nitrogen isotopic cycles. By reproducing the observed relationship between δ ¹⁵NO ₃ ⁻ and nitrate concentration using this model we found that most nitrate is transported horizontally from the eastern equatorial Pacific. We also conducted case studies and investigated the effects of differences in pathways of nitrate transport on the distributions of δ ¹⁵NO ₃ ⁻ and nitrate concentration. From these studies we concluded that the observed linear relationships between δ ¹⁵NO ₃ ⁻ and ln[NO ₃ ⁻ ], having a common slope around 6‰ but different intercepts at each station, are evidence of the significant horizontal transport of nitrate to the surface water in this area.  相似文献   

Roles of Physical Processes in the Carbon Cycle Using a Simplified Physical Model     

Masahiko Fujii  Motoyoshi Ikeda  Yasuhiro Yamanaka 《Journal of Oceanography》2000,56(6):655-666

A simplified physical model is proposed in this article to describe differences among basins in substance distributions which were not well described by previous simplified models. In the proposed model, the global ocean is divided into the Pacific/Indian Ocean (PI), the Atlantic Ocean (AT), the Southern Ocean and the Greenland/Iceland/Norwegian Sea. The model is consisted of five physical parameters, namely the air-sea gas exchange, the thermohaline circulation, the horizontal and vertical diffusions, and the deep convection in the high-latitude regions. Individual values of these parameters are chosen by optimizing model distribution of natural ¹⁴C as a physical tracer. The optimal value for a coefficient of vertical diffusion in the low-latitude region is 7.5 × 10^–5 [m²s^–1]. Vertical transports by the Antarctic Bottom Water and the North Atlantic Deep Water are estimated at 1.0 Sv and 9.0 Sv. Global-mean air-sea gas exchange time is calculated at 9.0 years. Using these optimal values, vertical profiles of dissolved inorganic carbon without biological production in PI and AT are estimated. Oceanic responses to anthropogenic fluctuations in substance concentrations in the atmosphere induced by the industrialization and nuclear bomb are also discribed, i.e., the effects appear significantly in AT while a signal is extremely weak in PI. A time-delay term is effective to make the PI water older near the bottom boundary.  相似文献   

Characterization of Banded Iron Formations by Two-Dimensional XRF Imaging and XANES Analyses     

Masaya MATSUNAGA  Katsunori FUKUDA  Yasuhiro KATO  Izumi NAKAI 《Resource Geology》2000,50(1):75-81

Abstract: Synchrotron radiation-induced X–ray fluorescence (SR–XRF) and conventional X-ray fluorescence (XRF) analyses were applied to determine the distributions of iron, manganese, calcium, titanium, and silicon, and chemical forms of iron and trace manganese in three banded iron formation (BIF) samples. The XRF imagings on the weathered and altered BIF from the Cleaverville Formation (3. 3–3. 1 Gyr), Western Australia, showed redistributions of iron, calcium, and manganese with the disappearance of the primary bandings, while, in contrast, titanium preserved its primary depositional distribution. The XRF imagings on the BIF from the Hamersley Group (2. 5 Gyr), Western Australia, showed that manganese and titanium distribute originally at boundary region between the iron-rich mesoband and the silica-rich mesoband. The X-ray Absorption Near Edge Structure (XANES) analysis revealed that the chemical forms of manganese and iron well represent the rhythmic change of the bandings.  相似文献   

Influence of export rain ratio changes on atmospheric CO<Subscript>2</Subscript> and sedimentary calcite preservation     

Megumi O. Chikamoto  Katsumi Matsumoto  Yasuhiro Yamanaka 《Journal of Oceanography》2009,65(2):209-221

The responses of atmospheric pCO₂ and sediment calcite content to changes in the export rain ratio of calcium carbonate to organic carbon are examined using a diffusion-advection ocean biogeochemical model coupled to a one-dimensional sediment geochemistry model. Our model shows that a 25% reduction in rain ratio decreases atmospheric pCO₂ by 59 ppm. This is caused by alkalinity redistribution by a weakened carbonate pump and an alkalinity increase in the whole ocean via carbonate compensation with decreasing calcite burial. The steady state responses of sedimentary calcite content and calcite preservation efficiency are rather insensitive to the deepening of the saturation horizon of 1.9 km. This insensitivity is a result of the reduced deposition flux that decreases calcite burial, counteracting the saturation horizon deepening that increases calcite burial. However, in the first 10,000 years the effect of reduced calcite deposition on the burial change is more prominent; while after 10,000 years, the effect of saturation horizon deepening is more dominant. The lowering of sediment calcite content for the first 10,000 years is effectively decoupled from the 1.9 km downward shift of the saturation horizon. Our results are in part a consequence of the more dominant role that respiration CO₂ plays in sediment calcite dissolution over bottom water chemistry in our control run and support the decoupling of calcite lysocline depth and saturation horizon shifts, as suggested originally by Archer and Maier-Reimer (1994) and Archer et al. (2000).  相似文献   

Encystment and excystment of <Emphasis Type="Italic">Gyrodinium instriatum</Emphasis> Freudenthal et Lee     

Tomoyuki Shikata  Sou Nagasoe  Tadashi Matsubara  Yasuhiro Yamasaki  Yohei Shimasaki  Yuji Oshima  Takuji Uchida  Ian R. Jenkinson  Tsuneo Honjo 《Journal of Oceanography》2008,64(3):355-365

In the present study, we have investigated the conditions influencing encystment and excystment in the dinoflagellate Gyrodinium instriatum under laboratory conditions. We incubated G. instriatum in modified whole SWM-3 culture medium and in versions of modified SWM-3 from which NO₃ ⁻, PO₄ ³⁻, NO₃ ⁻ + PO₄ ³⁻, or Si had been omitted and observed encystment. Percentage encystment was high in the media without N and without P, while the percentage encystment in the medium lacking both N and P was highest. Moreover, to investigate N or P concentration which induced the encystment, Gyrodinium instriatum was also incubated in media with different concentrations of inorganic N and P; the concentrations of NO₂ ⁻ + NO₃ ⁻ and PO₄ ³⁻ were measured over time. The precursors of cysts appeared within 2 or 3 days of a decrease in NO₂ ⁻ + NO₃ ⁻ or PO₄ ³⁻ concentration to values lower than 1 μM or 0.2 μM, respectively. When cysts produced in the laboratory were incubated, we observed excystment after 8–37 days, without a mandatory period of darkness or low temperature. We incubated cysts collected from nature at different temperatures or in the dark or light and observed excystments. Natural cysts excysted at temperatures from 10 to 30°C, in both light and dark, but excystment was delayed at low temperatures. These studies indicate that G. instriatum encysts in low N or P concentration and excysts over a wide temperature range, regardless of light conditions, after short dormancy periods.  相似文献   

O<Subscript>2</Subscript> consumption rate and its isotopic fractionation factor in the deep water of the Philippine Sea     

Noriko Nakayama  Yasuhiro Yamanaka  Toshitaka Gamo 《Journal of Oceanography》2008,64(3):451-457

Concentration and stable isotopic compositions (δ ¹⁸O) of dissolved O₂ were measured in seawater samples collected from the Philippine Sea in June 2006. The in-situ O₂ consumption rate and the isotopic fractionation factor (α _r ) during dissolved O₂ consumption were obtained from field observations by applying a vertical one-dimensional advection diffusion model to the deep water mass of about 1000–4000 m. The average O₂ consumption rate and α _r were, respectively, 0.11 ± 0.07 μmol kg⁻¹yr⁻¹ and 0.990 ± 0.001. These estimated values agree well with values from earlier estimations of Pacific deep water. The in-situ O₂ consumption rates are two or more times higher north of 20°N, although the value of α _r was not significantly different between the north and south. Its levels varied rapidly in the water mass of less about 2000 m depth. These results suggest that organic matter from the continent imparts a meaningful contribution to the upper water in the northern part of the area; it might produce the strong O₂ minimum that is evident in the water mass from about 1000–2000 m in the northern part of the Philippine Sea.  相似文献   

Distribution of nitrate in groundwater affected by the presence of an aquitard at an agricultural area in Chiba, Japan     

Tatsuhiro Nishikiori  Takejiro Takamatsu  Ayato Kohzu  Yasuhiro Nakajima  Mirai Watanabe 《Environmental Earth Sciences》2012,67(5):1531-1545

Geological and geographical parameters including land use, stratigraphic structure, groundwater quality, and N- and O-isotopic compositions of nitrate in groundwater were investigated to elucidate the mechanism of groundwater pollution by NO₃ ^? in the agricultural area of Katori, Chiba, Japan. An aquitard distributed in the western part of the study area has produced two unconfined aquifers. The average concentrations of NO₃ ^? and dissolved oxygen (DO) were high in the aquifer above the aquitard (7.5 and 7.6 mg/L, respectively) and in the aquifer of the eastern part of the study area that was not influenced by the aquitard (11.9 and 7.8 mg/L, respectively); however, the levels in the aquifer under the aquitard were relatively low (2.2 and 3.7 mg/L, respectively). The δ¹⁵N and δ¹⁸O values of NO₃ ^? generally increased exponentially in the groundwater that flowed into the aquifer under the aquitard as the concentration of NO₃ ^? decreased, although this decrease in NO₃ ^? also occasionally occurred without isotopic changes. These results indicated that the aquitard prevented the penetration of NO₃ ^?, DO, and gaseous O₂. Under the aquitard, denitrification and dilution with unpolluted water that entered from natural forested areas reduced the NO₃ ^? concentrations in the groundwater. The major sources of NO₃ ^? in groundwater in the study area were estimated to be NH₄-chemical fertilizer, livestock waste, and manure.  相似文献   

Erratum to: Temperature scaling pattern dependence on representative concentration pathway emission scenarios     

Yasuhiro Ishizaki  Hideo Shiogama  Seita Emori  Tokuta Yokohata  Toru Nozawa  Tomoo Ogura  Manabu Abe  Masakazu Yoshimori  Kiyoshi Takahashi 《Climatic change》2014,125(2):277-277

  相似文献   

MEAN SEA LEVEL AND SEA SURFACE VARIABILITY OF NQRTHWEST PACIFIC OCEAN AND EASTERN CHINA SEAS FROM GEOSAT ALTIMETRY   总被引：1，自引：0，他引：1  

陈戈  贺明霞 《中国海洋湖沼学报》1994,12(2):154-164

Collinear analysis technique is widely used for determining sea surface variability with Geosat altimeterdata from its Exact Repeat Mission(ERM).But most of the researches have been only on global scaleor in oceans deeper than 2000 m.In shallow shelf waters this method is hampered by the inaccuracy ofocean tide data supplied with Geosat Geophysical Data Records(GDRs).This work uses a modified collinearanalysis technique characterized by simultaneous separation of mean sea level and ocean tide with theleast squares method,to compute sea surface variability in the Northwest Pacific Ocean and eastern ChinaSeas.The mean sea level map obtained contains not ouly bathymetric but also dynamic features such asamphidromes,indicating considerable improvement over previous works.Our sea surface variability mapsshow clearly the main current system,the well-known Zhejiang coastal upwelling,and a northern East Chi-na Sea meso-scale eddy in good agreement with satellite sea surface temperature(SST)observation and his-to  相似文献   

The Ejection of Relativistic Bullets from Supernovae and the Generation of Gamma-Ray Bursts     

Umeda H 《The Astrophysical journal》2000,536(2):L89-L92

We present 1 μm Hubble Space Telescope/near-infrared camera and multiobject spectrometer resolved imaging polarimetry of the GG Tau circumbinary ring. We find that the ring displays east-west asymmetries in surface brightness as well as several pronounced irregularities but is smoother than suggested by ground-based adaptive optics observations. The data are consistent with a 37 degrees system inclination and a projected rotational axis at a position angle of 7 degrees east of north, determined from millimeter imaging. The ring is strongly polarized, up to approximately 50%, which is indicative of Rayleigh-like scattering from submicron dust grains. Although the polarization pattern is broadly centrosymmetric and clearly results from illumination of the ring by the central stars, departures from true centrosymmetry and the irregular flux suggest that binary illumination, scattering through unresolved circumstellar disks, and shading by these disks may all be factors influencing the observed morphology. We confirm a approximately 0&farcs;25 shift between the inner edges of the near-infrared and millimeter images and find that the global morphology of the ring and the polarimetry provide strong evidence for a geometrically thick ring. A simple Monte Carlo scattering simulation is presented that reproduces these features and supports the thick-ring hypothesis. We cannot confirm filamentary streaming from the binary to the ring, also observed in the ground-based images, although it is possible that there is material inside the dynamically cleared region that might contribute to filamentary deconvolution artifacts. Finally, we find a faint fifth point source in the GG Tau field that, if it is associated with the system, is almost certainly a brown dwarf.  相似文献